Stiffness-determining device



May 18, 1965 w. A. GURNEY ETAL 3,183,707

STIFFNESS-DETERMINING DEVICE Filed Dec. 1. 1961 5 Sheets-Sheet 1 1771ve?? 70m May 18, 1965 w. A. GURNEY ETAL 3,183,707

STIFFNESS-DETERMINING DEVICE Filed Deo. 1. 1961 5 sheets-sheet z Q ff e'19 0 0! f7] f l? May 18, 1965 w. A. GURNEY ETAL 3,183,707

STIFFNESS-DETERMINING DEVICE Filed Dec. 1. 1961 5 Sheets-Sheet 5 0 l 27'e 9! /fa f:

"ft/4 M .In ve rfi-5w May 18, 1965 w. A. GURNEY ETAL 3,183,707

STIFFNES S-DETERMINING DEVICE May 18, 1965 Filed Dc. 1. 1961 W. A.GURNEY ETAL STIFFNESS-DETERMINLNG DEVICE 45- Sheets-Sheet 5 `I71re7175hs4U/[arq 14, Gurn? ArThurTf. Sfh b5 me 7%@ United States Patent() Claimspriority, application Great Britain, Bec. 2b, i966,

43,6s1/6s ii claims. (ci. 1s-15.6)

This invention relates to a stiffness-determining device for testingyieldable materials, and especially for testing the state of cure ofmaterials such as vulcanizable rubber compositions as they are heated toeffect Vulcanization.

According to the invention, a stiffness-determining or cureatestingdevice comprises a framework, an inextensible sandwich strip forembedding within a sample of material in respectl of which thevstiffness is to be determined or the 4cure is to be tested, a clampfixed to the framework and located on each side of the strip forclamping the said sample, opposed springs connected one to each end ofthe strip, oscillation means connected to the strip, means for limitingthe amplitude of movement of the strip, and means for recording theforce applied to oscillate the strip between the limits of amplitude.

A device for determining the stiffness or testing the cure of a sample,constructed in accordance with the invention, enables small samples ofthe material to be tested and since the movement of the strip is onlysmall when such samples are tested, then it is preferred to incorporatean amplifying means in the device to amplify the movement of the stripwhen recorded.

The device preferably includes a beam member pivotally mounted on apivot on said framework and connected to said strip and adapted tooscillate through a predetermined amplitude. One end of the strip isalso connected to a spring connecting said strip to said oscillationmeans. The other end of the strip can be connected to a second springacting in opposition to the firstmentioned spring. In any case, Vatleast one end of the strip must be connected to the beam member whichforms the connection to the respective spring, and the two springs aremounted in opposition. For instance, the springs can be mounted on thebeam member on the same side of the pivot but in opposite directions, orcan'be mounted one on each side of the pivot to act in the samedirection on the beam member so that as the beam member pivots, themovement is restrained by one of the springs.

The means to limit the amplitude of movement of the strip can be a stoplocated to abut the strip when it moves lto a predetermined position orcan be located to abut the Preferably, a pair of stops are providedVbearn member. adjacent one end of the beam member to limit the amplitudeof movement thereof and positioned at a greater distance from the pivotthan the distance between the point of attachment of the strip to thebeam member and the pivot.

The device, according to the invention, can include any type ofrecording means for recording the force applied to oscillate the stripand can be, for example, an electrical transducer or can convenientlycomprise a recording device of the type described and claimed in ourco-pending U.S. application Serial No. 156,216. Such a recording deviceconsists essentially of an electrical recording circuit energised inresponse to movement of the strip or beam member to a predeterminedposition spaced from the resting position in the direction ofoscillation of the strip of beam member, and recording means actuated byenergization of the recording circuit so as to record the part of theperiod of oscillation which elapses before the strip reaches thepredetermined position. The recording BSB'? AEstimated May i8, 1965means which is of particular use in this invention, comprises anelectrically-conductive support for electro-sensitive paper, anelectrically-conductive stylus mounted for oscillation through apredetermined amplitude in response to said means, and means for movingthe paper transversely of the direction of movement of the stylus, thesupport and stylus being connected in the electrical recording circuit.Generally, said stylus is mounted on the spring connected to theoscillation means, but it may be mounted on the other spring, ifdesired. Preferably, the electrical recording circuit is energised whenthe strip or beam member is moving between its limits of amplitude, andwhen the strip or beam member abuts the stop or pair of stops, anelectrical circuit is closed so that the recording means is inoperative.As the strip or beam member moves between its limits of amplitude, thenthe stylus forms Ya trace on the electro-sensitive paper which indicatesthe force applied to the strip or beam member to oscillate it betweenits limits of amplitude.

The means for oscillating said strip or beam member can be any suitableknown type, but preferably is mechanical means such as a crank or othereccentric connected to the rst-mentioned spring.

A device constructed in accordance with the invention is particularlyuseful for testing the state of cure of a vulcanizable rubbercomposition or other curable composition in which a sample of thematerial to be tested is clamped between platens to heat said sample toeffect vulcanization or curing thereof. The platens can be heated by anysuitable meanssuch as by steam and electrical heating elements. As thesample is heated, then the stilfness increases requiring an increasedforce to be applied to oscillate the beam member or strip, and the tracemade by the stylus'indicates the increased stiness.

One form of stiffness-determining deviceconstructed according to theinvention for use in determining Vthe state of cure of a sample ot'avulcanizable composition, will now be described by way of example Vwithreference to the accompanying drawings, in which:

FIGURE l is a front elevation of the device, part of which is shown insection,

FIGURE 2 is a perspective view of one end of the beam member,

FIGURE 3 is a perspectiveV view of the inextensible strip and clampingmeans,

FIGURE 4 is an end-view of the device,

FIGURE 5 is a sectional elevation on the line A-A of FIGURE l, and

FIGURE 6 is a circuit diagram for the recording means.

The device consists of a beam member 1 formed by two spaced'limbs Z, 3pivotally mounted on a framework 4 `by a support member 5, FlGURE 1shows the beam member l with the front limb 2 removed. The supportmember 5 consists of an L-shaped member 6 secured to the framework 4 anda facing plate 7, each chamfered as at S to be downwardly pointed. APhosphor bronze strip 9 is retained between the L-shaped member 6 andthe facing plate 7 by screws 10 and is secured ashort distance belowsaid support member 5 to the horizontal upper surface of a supportingblock 11 fixed transverse of the beam member l adjacent its end. Achamfered plate l2 locates the Phosphor bronze strip 9 on the supportingblock Ill and the Phophor bronze strip permits the beam member 1 topivot about the supporting member 5. The Phosphor bronze strip 9 extendsdownwardly of the beam member l and is secured to a link member 13.

The link member 13 consists of two spaced parallel rods i4, l5, eachconnected at one end to a transverse member lo in a slot of which issecured the end of the Phosphor bronze strip 9 by means of plate i7. Therods en n.9

14, l hang perpendicularly from the beam member l, when in the restingposition, and are connected at their other ends to a further transversemember 18 which is provided with a peg l@ engaging one end of aperforated inextensible strip Ztl of Invar steel or other lightnonextensible material. The other end of strip Ztl is located on a peg2l provided on a transverse member 22 connected to a coil spring 23. Theother end of spring 23 4is secured to a tension adjusting meansconsisting of a threaded rod 24 and a nut 25 which is retained by aframe member 26. The link member, strip and coil spring are shown insection. If desired, the transverse ensayo? and gear-box 67 by means ofshaft 68 which is drive by means of a further electric motor (not shown)which will be referred to hereinafter as the chart motor and isschematically shown in FGURE 6 as 81. The roller 65 as it rotates servesto draw the electro-sensitive paper 64 from the roller 65 at a constantspeed. A pressure roller 69 is also secured to the framework to maintainthe paper in contact with roller 65 and this pressure roller 69 isindicated as shown.

A locating cam 70 is rotatable on a shaft to locate the beam member l ina central resting position between the l stops 46, 47 as shown in FIGUREl. VThe locating cam member 22 can be carried on a retaining leverpivoted yto a frame member which is connected to said spring V23 tofacilitate easy fitting of the strip 2;@ on pegs i9, 2l. Clamping meansare provided on each side of the strip and these are shown in section inFIGURE l. The ,clamping means comprise a pair of platens 27, 28, one,27, of which is secured to the framework 4. Each platen is provided with,electrical heating means 27', 28 and surrounded on five faces withheat-insulating material 29, 30. `The outer platen 28 is axially movablewith respect to the other platen 27 and is carrie'don a plate 3l securedto a further plate 32 being captive means for 'the end of a threaded rod33. This rod 33 engages a bar 34 of a pair of support members 35 and canbe screwed axially inwardly or outwardly of the bar 34 by means of wheel36 (shown in full) to move the platen 2l?? and insulating materialtowards or away from the other platen 27. The support members arepivotally secured on their lower ends to a frame member 37 to permit theplaten 28 to be swung clear of the strip Ztl Vto facilitate fittingthereof and when the support mem- --bers 35 are in the closed positionas indicated in FIGURE l, they are retained by a latch 38. As shown inFIGURE 3 the outer platen 28 is provided on its inner face with twostrips 39, 4t) which Vdeiine a slot 41 andthe portion of the face of theplaten 28 forming theV base 42 of the slot 41 is provided with series ofsaw-tooth serrations. The inner face of the other platen 2'/V isprovided with a series of-serrations 43 corresponding in position tothose of platen 27.

The beam `member terminates, at the end opposite to vthe pivoted end, ina rod 44 of electrical insulation material which carries a shortVmetal'rod 45 positioned ,to contact a pair of stops 46, 47 ofelectrically-conductive material at the limits ofamplitude of movementof the beam member 1. The stops 46, 47 are positioned at such a distanceapartA that the overall vertical movement of the strip 20 when the beammember pivots, is of the order of l0 thousandths of an inch. The shortmetal rod' 4S is also connected by means of a piece of fine flexibleWire 48 to a terminal Y4S", this wire 4S offering no substantialresistance to movement of the beam member Il.

V57 on the shaft of a variable speed gear-box 5S driven by an electricmotor 59. The crank 57 is secured to a cam 60 having a cam surfaceextending through 180 degrees. A cam switch 6l is mounted on theframework 4 to be operated by the cam surface as it rotates. TheelectricA motor 59 will be referred to hereinafter as the A turntable 62is mounted by means ofsupport member V63 to said framework 4 and isadapted to carry a roll of electro-sensitive paper 64, the end of whichpasses through a vertical slot in the framework 4 over roller 54 and afurther roller 65 driven through a coupling' 66 connected in parallel tothe mains.

lthe vulcanization temperature.

moved from its rmid position to close switches 85, 86 and 7? is providedwith an arm 7l to which is secured a knob '72 to facilitate rotation ofthe locating cam 70. Rotation of the locating cam 70 is also arranged toclose a pair of coupled microswitches to energise the pen motor 59 andthe chartY motor Si and also the electrical record- Ving circuit. Y

FEGURE 6 is a circuit diagram of the recording device and consists, asshown, of a transformer 80, the primary coil of which is supplied by themains through a mains switch, r:The pen motor 59 and the vchart motor 81are The transformer is arranged so as to provide a high tension circuitfor a triode valve S2, the anode of which is connected through avariable resistance to the electrically-conductive stylus 53 carried soas to transverse the electrically-conductive roller 54 which isconnected to the framework of the device. The transformer Si) is tappedmidway along its secondary coil to provide a voltage of volts at the twostops 46, 47 which the beam member l abuts at its limits of amplitude.When the beam member 1 abuts either of the stops 46, 47, then a negativevoltage is applied to the grid of the triode valve via the short metalrod 46 and terminal 49 to prevent currents iiowing through the valve toground via the roller 54. l The half-wave jrectier is included inhightension circuit of the valve and a further half-wave rectifier isincluded in the circuit of the beam member l' and each halfwaverectilieris provrded'with a smoothing condenser. The device is further providedwith a stylus 83 controlled by a switch S4 'to mark theelectro-sensitive paper 64 periodically, and 4usually the paper ismarked at minute intervals.

t-o allow the beam member l to move freely. The pen motor and chartmotor are both brought into operation and the crank 57'rotates about itsshaft member to oscillate the carriage 5l on the rod 52. The spring Silis thereby oscillated, causing the beam member 1 to oscillate betweenthe stops 46, 47.` At the same time, the electrosensitive paper 64 isslowly moved over the roller 54 by means of rollers 65, 69. As the beammember oscillates,

the strip 20 oscillates within the sample `lili) and since this isclamped securely to the strip 20, `the oscillations of the strip bringabout deiiection on the samplel 160. When the beam member 1 is movingbetween the contacts 46,

' 47, there is no negative voltage applied to the grid of the triodevalve and desired discharge through the valve is permitted so that thestylus 53 records a line vertically `on the electro-sensitive paper 64.When the beam mem- 4ber l abuts either of the stops l46, 47 then anegative voltage is applied to the grid of the valve, preventingdischarge through the valve so that no trace is recorded on theelectro-sensitive paper. As the sample of rubber composition becomesvulcanized, the stiffness of the composition increases and theresistance to deflection also increases, requiring an increased force tooscillate the beam member 1 between the two contacts 46, 47. The forceapplied by spring 50 to move the beam member 1 from stops 46, 47increases as vulcanization proceeds and this is recorded as a line ofincreasing length on the electrosensitive paper 64.

The recording device records a series of lines corresponding to therespective upward and downward movement of the beam member 1. However,due to hysteresis yof the sample of rubber composition, the lines of therespective series are relatively displaced, giving a shading effect onthe record. If it is desired to record when the beam member is moving inonly one of its directions, then the cam switch 61 is arranged to closewhen the beam member is moving in the other direction. For instance,should it not be desired to record upward movement of the beam member,then the cam switch 61 is ar'- ranged to close when the carriage 51begins its upward movement from the bottom of the rod 52 so that eventhough the beam member is between the stops 46, 47 the negative voltageis still applied to the 'grid to prevent discharge through theelectro-sensitive paper 64. The cam switch 61 can be coupled in serieswith a further switch 87 which is closed should it be desired to makeuse of the cam switch 61. The cam switch 6.1 and further switch 87 areboth connected parallel with the stops 46, 47 and terminal 49. The linesrecorded vby the recording device lengthen to a maximum as thevulcanization is completed.

Since the stiffness-determining device provides a comparative record ofthe force absorbed by the yieldable material, the reproducibility ofresults obtained from a number of devices, according to the invention,is good, and thermal eiects do not substantially alter the length of thelines recorded. The movement of the inextensible strip of the materialsto be tested is very small .with the result that inaccuracy due to tear,is obviated.

In an alternative form of an electrical circuit to energise therecording means, the beam member opens the electrical circuit when itcontacts the stops to prevent the flow of electricity to the recordingmeans. For instance, the beam member can be made to abut the respectivestop at its limits of amplitude and also to open a switch comprising apair of spring leaves which are connected to a transformer when thebeammember is Vmoving between the stops.

rl`he coil spring 23 secured to one end of the strip can be replaced, ifdesired, by a suitably-positioned leaf spring.l

Having now described our invention, what we claim is:

l. A stiffness-determining or cure-testing device comprising aframework, an inextensible sandwich strip adapted to be embedded withina sample of material of which the stillness is to be determined or thecure is to tested, a clamp fixed to the framework and located on eachside of the strip for clamping the said sample therein,

a beam member pivotally mounted on a pivot on said framework andconnected to one end of said strip, a stop means to limit the amplitudeof movement of said beam member, oscillation means disposed `contiguoussaid beam member, a first spring connected between said beam member andsaid oscillation means to impart oscillations to said beam member, asecond spring connected to the other end of said strip to act inopposition to said iirst spring, and means operatively connected to saidoscillation means for recording the force applied to oscillate thestrip.

2. A device according to claim l in which means to adjust the tension inthe second spring are provided between said `framework and the end ofthe spring secured thereto.

3. A device according to claim l in which said stop means include twostops provided on said frame-work located one 0n each side of the beammember adjacent one end thereof.

4. A device according to claim 3 in which the distance between saidstops and the pivot is greater than the distance between the point ofattachment of the strip to the beam member and the pivot.

5. A device according to claim l in which said oscillation meanscomprise an eccentric.

6. A device according to claim l in which said means for recording Ithe`force applied to said strip comprises an electrical recording circuitenergised in response to movement of said beam member to a predeterminedposition spaced from the resting position in the direction ofoscillation of the beam member, and recording means actuated byenergisation of the electrical recording circuit to record the part ofthe period of oscillation which elapses before the beam member reachesthe predetermined position.

7. A device according to claim 6 in which the recording means comprisesan electrically-conductive support for electro-sensitive paper, anelectro-conductive stylus mounted for oscillation through apredetermined amplitude in response to a said means which osciilates thebeam member, and means for moving the paper transversely of thedirection of movement of the stylus, .the support and the stylusconnected in the electric recording circuit.

8. A devicegaccording to claim 6 in which said electrical recordingcircuit is energised when said beam member is free of said stop means.

9. A cure-testing device for testing the state of cure of a vulcanizablerubber composition comprising a framework, an inextensible sandwichstrip adapted to be ernbedded within a sample of vulcanizable rubbercomposltion, a pair of platens mounted on the framework and located oneon each side of the strip for clamping the said sample therebetween,heating means to heat said platens, a beam member pivotally mounted on apivot on said framework and pivotally secured at one end to one end ofsaid strip, a spring connected between the other end of said strip andsaid framework, oscillation means disposed contiguous said beam member,a further spring connected between said beam member and said oscillationmeans to impart oscillations to said beam member, a pair of stopslocated on said `framework and positioned one on each side of and at theend of said beam member opposite to that secured to said strip to limitthe amplitude of movement of said beam member, and means operativelyconnected to said oscillation means to record the force applied tooscillate said beam member.

l0. A cure-testing device according to claim 9 in which said heatingmeans are electrical heating elements to effect the heating of saidplatens.

l1. A device for ,following the vulcanization of a sarnple of a rubbercomposition as it is vulcanized which cornprises a framework, a beammember, a pivot provided on said framework on which the beam member ispivotally mounted adjacent one end, a rst spring connected to said beammember intermediate its other end and the pivot, means to alternatelyelongate and relax said spring to oscillate said beam member, stop meansto limit the arnplitude of movement of the beam member, a substantiallyineXtensible strip pivotally connected at one end to the end of the beammember adjacent the pivot, a clamp secured to said lframework andlocated on each side of the strip for clamping a sample of rubbercomposition in contact with both sides of the strip, means to heat therubber composition to efect vulcanization thereof, a second springconnected at one end to the other end of the strip and secured at itsother end to the framework so as to act in opposition to the firstspring, an electricallyconductive support for electro-sensitive paper,an electroconductive stylus mounted on a carriage secured for movementwith said first spring to traverse said paper, and an electrical circuitincorporating said stop means and said stylus energized when said beammember is not in contact with said stop means `to record a line on saidpaper whereby a line of increasing length up to `a maximum is obtainedwhen said rubber composition is heated to eiiect vulcanization.

(References on following page)

11. A DEVICE FOR FOLLOWING THE VULCANIZATION OF A SAMPLE OF A RUBBERCOMPOSITION AS IT IS VULCANIZED WHICH COMPRISES A FRAMEWORK, A BEAMMEMBER, A PIVOT PROVIDED ON SAID FRAMEWORK ON WHICH THE BEAM MEMBER ISPIVOTALLY MOUNTED ADJACENT ONE END, A FIRST SPRING CONNECTED TO SAIDBEAM MEMBER INTERMEDIATE ITS OTHER END AND THE PIVOT, MEANS TOALTERNATELY ELONGATE AND RELAX SAID SPRING TO OSCILLATE SAID BEAMMEMBER, STOP MEANS TO LIMIT THE AMPLITUDE OF MOVEMENT OF THE BEAMMEMBER, A SUBSTANTIALLY INEXTENSIBLE STRIP PIVOTALLY CONNECTED AT ONEEND TO THE END OF THE BEAM MEMBER ADJACENT THE PIVOT, A CLAMP SECURED TOSAID FRAMEWORK AND LOCATED ON EACH SIDE OF THE STRIP FOR CLAMPING ASAMPLE OR RUBBER COMPOSITION IN CONTACT WITH BOTH SIDES OF THE STRIP,MEANS TO HEAT THE RUBBER COMPOSITION TO EFFECT VULCANIZATION THEREOF, ASECOND SPRING CONNECTED AT ONE END TO THE OTHER END OF THE STRIP ANDSECURED AT ITS OTHER END TO THE FRAMEWORK SO AS TO ACT IN OPPOSITION TOTHE FIRST SPRING, AN ELECTRICALLYCONDUCTIVE SUPPORT FORELECTRO-SENSITIVE PAPER AN ELECTROCONDUCTIVE STYLUS MOUNTED ON ACARRIAGE SECURED FOR MOVEMENT WITH SAID FIRST SPRING TO TRAVERSE SAIDPAPER, AND AN ELECTRICAL CIRCUIT INCORPORATING SAID STOP MEANS AND SAIDSTYLUS ENERGIZED WHEN SAID BEAM MEMBER IS NOT IN CONTACT WITH SAID STOPMEANS TO RECORD A LINE ON SAID PAPER WHEREBY A LINE OF INCREASING LENGTHUP TO A MAXIMUM IS OBTAINED WHEN SAID RUBBER COMPOSITION IS HEATED TOEFFECT VULCANIZATION.